Motor preparation in postural control in seated spinal cord injured people

Spinal cord injured (SCI) people try to compensate for the loss of postural muscle function by increased use of non-postural muscles. Such alternative muscle use, however, may necessitate important modifications in motor control. In this study motor programming processes were investigated in three groups, i.e. in high thoracic SCI, low thoracic SCI and non-SCI subjects. A bimanual forward-reaching task, in which graded sitting balance perturbation was systematically invoked, was presented to the subjects as a visual precue choice reaction time (RT) task. Effects of movement preparation were examined by precuing reaching distance information. RT and movement times were recorded. Centre of pressure (CP) displacement was used as an indicator for sitting balance perturbation. Results indicated that high thoracic SCI subjects programmed balance-perturbing reaching movements as fast as did non-SCI subjects. Low thoracic SCI subjects, on the other hand, showed substantially longer programming times. This latter outcome is consistent with the hypothesis that the low thoracic SCI subjects adopted a more complex postural control strategy involving residual motor functions in an attempt to actively compensate for loss of postural muscle function. High thoracic SCI subjects, on the other hand, appeared to adopt a less complex and thus easier to programme postural control strategy.